This invention relates to core drills used in drilling holes in concrete, hard fired brick and the like, and more particularly to provision of means for extending the effective length of a core drill.
The drilling of lengthy holes, e.g., holes 10-20 inches long, in structures or structural components made of concrete or other dense masonry materials is commonly accomplished with a core drill (also called xe2x80x9ccore drill bitxe2x80x9d). A typical core drill comprises an elongate hollow tubular member, one end of which is adapted to be releasably secured to the rotatable output shaft of a portable driver which typically is electrically powered but which may also be powered by a compressed gas such as air. Affixed to the opposite end of the tubular member, usually by welding, is a tubular cutting head or bit that may comprise diamond or carbide particles embedded in a metal matrix. The core drill derives its name from the fact that as it drills into concrete or other dense material the interior of the drill fills with a solid core of the material that is being drilled. Typically water is injected into the core drill to facilitate the drilling process. When water is injected, the drilling process is identified as xe2x80x9cwet coringxe2x80x9d.
A problem with using core drills is that different length drills are required if different length holes are to be drilled. For that reason, manufacturers sell core drills in a number of different lengths. However, core drills are expensive and have a limited useful life. Having a full complement of different length core drills is costly and, even then, the appropriate length drill may not be available, or it may be available but worn to the point of being effectively useless. In such case, a longer length drill, if available, may be used to perform the desired drilling operation. Otherwise, since a shorter length drill will not suffice, the drilling operation may need to be delayed pending availability of a drill of suitable length.
The primary object of this invention is to provide an improved means of extending the effective length of a core drill used for drilling holes in concrete and other dense masonry material.
Another object is to provide a novel apparatus for extending the effective length of a core drill of the type having a screw connector for connecting it to a driver.
Still another object of this invention is to provide an extender for a core drill that is designed to be disposed between and to make screw connections to a driver and a core drill.
A further object is to provide an apparatus for extending the effective length of a core drill that comprises an extender tube attachable to a driver and a connector assembly for attaching the extender tube to a core drill, the connector assembly comprising an expandable means for releasably locking the connector assembly to the extender tube.
The foregoing objects are achieved by providing an extender apparatus for a core drill that comprises an elongate extender tube having an open front end and a back end that is adapted to make a secure but releasable connection to an electrical or pneumatic driver, and a connector assembly releasably mounted in the front end of the extender tube. In a preferred embodiment of the invention, the connector assembly comprises a mandrel that has a center passageway, a threaded axial extension in the form of a hollow shaft is mounted in one end of the mandrel, and an expandable locking sleeve that surrounds the mandrel and cooperates therewith to lock the mandrel to the extender tube. The mandrel has a tapered outer surface whose diameter increases with increasing distance from the mandrel end having the threaded axial extension, and the sleeve is made so that moving it relative to the mandrel in the direction of increasing mandrel outer surface diameter will cause the sleeve to expand radially and into tight frictional engagement with the mandrel and the extender tube. The threaded axial extension is adapted to make a screw thread connection to a core drill having a threaded hole or connector at its back end, thereby making the extender tube an extension of the core drill so that the latter can drill a hole with a depth greater than the length of the core drill (of course, drilling is interrupted when the depth of the drilled hole is near the length of the core drill for the purpose of removing the core of particles produced by the drilling). After drilling has been completed, detachment of the extender apparatus is easily accomplished without use of special tools.